<html lang="zh-Hans">
<head>
  <meta charset="UTF-8" />
  <title>Document</title>
  <style>
    body div #my_id {
      width: 100px;
      height: 100px;
      background-color: #ff5000;
    }

    body div img {
      width: 30px;
      height: 30px;
      background-color: #ff1111;
    }
  </style>
</head>
<body>
  <div>
    <img id="my_id" class="my_class"/>
    <img />
  </div>
</body>
</html>